Torrefaction of biomass: Production of enhanced solid biofuel from municipal solid waste and other types of biomass

The rapid increase in population has been identified as one of the main reasons for the abundance generation of municipal solid waste (MSW), which could be advantageous when converted to energy. Utilizing MSW as a renewable fuel in waste-to-energy conversion technologies provides solutions to depleting fossil fuel reserves, reduces the effect of pollution on human health, and reduces the pressure on land for landfills. The urgent interest in renewable energy generation has recently promoted the utilization of MSW as a renewable and sustainable fuel for thermochemical processes, which is in line with the United Nations' low carbon footprint targets. However, to efficiently harness MSW as fuel for combustion, pyrolysis, and gasification, curbing limitations, such as high moisture content, low calorific value, poor grindability, poor combustion characteristics, low energy density, low H/C and O/C ratios of the MSW is paramount. An effective way to curb these is to pretreat the MSW. Torrefaction is a greener and promising thermochemical process frequently applied for pre treating different biomass resources to curb the MSW limitations. Nonetheless, this process is yet to be profoundly described for MSW and other types of biomass. Therefore, in this review, the influence of torrefaction process parameters on the properties of MSW and other types of biomass was evaluated. The properties of MSW as a raw material for torrefaction process were also presented. Furthermore, the classification of different types of reactors for torrefaction process and potential applications of the torrefied MSW (solid biofuel) were discussed.